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Portable Hydraulic Riveter.                     315

boiler seam being placed between w and M, the rivet heated
and put in from the side M ; lever H opens valve p to pressure,
and a right-hand advance is given to the ram x, due to the
difference of area of its faces. This pressure, assisted by the
head of water passing from the tank, through the check-valves
Q and s, carries forward parts u and Y. When w and v reach
the rivet and plate respectively, lever G admits pressure water at
o through pipe A, to advance the ram u, thus pressing the
plates firmly together between tools v and M. And now valve
NT is opened by lever F, and pressure given to T in turn, thus
bringing forward the cylinder Y and the cupping tool w to
close the rivet, the pressure obtained being due to the difference
of areas of the rams u and x, part of the water from u passing
into T through pipe j. The pressure should be kept on the rivet
until it cools somewhat, to secure a tight joint, and the three
levers are then moved to exhaust, when the pressure b pushes
back ram x, bringing u and Y to normal position, and lifting the
water up L into the tank.

Fig. 298 shews all the later improvements introduced : the
plate closing (in 1880) and the use of low pressure water to
fill the cyliriders (in 1890). The latter is very interesting, and
greatly economises high pressure water, which is only used as a
film on the back of the tank water, as it were, the fluid being
practically Incompressible. The plate-closing apparatus prevents
* collars' being formed on the rivet between the plates. In a
loo-ton riveter, 60 tons are applied for cupping, while the
remaining 40 tons hold the plates together, but ultimately the
whole 100 tons is applied to the rivet-head and plates.

Portable Hydraulic Riveters.—Although Mr. Tweddell
introduced hydraulic riveting in 1865, his invention of the port-
able machine did not occur till 1871, from which date Messrs.
Fielding and Platt, who then took up its manufacture, were
associated with him in the design of nearly all his later
hydraulic machine tools. There are two forms of the portable
machine known as the * Direct Acting' and ' Lever' types re-
spectively; their present construction being shewn ;n Figs. 299
and 300. Referring to the former, frame A is a rigid casting,
supporting a cylinder B with direct-acting ram c. There are three